Example local environment around an A nucleus. Each open-shell TM ion in a ≈5 Å sphere around species A transfers a finite amount of unpaired electron spin density from its d orbitals to s orbitals on A, via bridging O 2p orbitals. This in turn results in a finite contribution to the overall Fermi contact shift of A. In this case, three TM–O–A spin density transfer pathways, P_i, can be distinguished, leading to different amounts of spin density transfer and therefore to different shift contributions.